I'm almost finished my 70s touring themed '79 GW. I found a NOS Windjammer on EBay that even came with the factory manuals - still in the plastic.

Having issues wiring the signals. The Vetter harness only has one lead for the front driving lights. On the naked GW the driving light turns off on the side that has a blinking signal. When I wire both of the fairing's driving lights to one of the bike's driving light wires I have a problem. If I'm signalling left, for example, the right driving light will blink dimly. Same on the other side. Ideally if I'm signalling left the right driving light should just stay steady at full power.

That sounds like a ground issue. I'd make sure that your grounding is good and solid. Check the pin connector that attaches to the fairing well for corrosion, etc. If you did the wiring of the harness to the bike, check it also especially at the splices where the harness was substituted for the original connections. If you didn't wire it, check it more importantly.

I noticed that the only ground on the Vetter harness is through the headlight connector. I'm going to follow your advice and maybe convert one of the extra wires in the harness to an additional ground.